The present invention relates to a demodulator and a timing regenerating device that is used in this demodulator.
As a conventional system of timing regeneration for a demodulator of a broadband digital radio communication system having a preamble signal analysis function, there has been one as described in Japanese Patent Application Laid-Open No. 8-46658.
This system focuses on the fact that the preamble signal has xc2xd of the frequency component of the symbol frequency (fs). Based on this, a correlation is obtained at the receiver side between the preamble signal and a xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t] output from a VCO (Voltage Control Oscillator). A timing phase is estimated from a vector angle of this correlation value.
Further, according to this system, sampling speed (i.e. sample/symbol) of the data is only 2. In the mean time, Japanese Patent Application Laid-Open No. 6-141048 discloses a system of estimating a timing phase from a correlation between a signal (for example, an envelope) after a nonlinear processing and a symbol frequency component exp [xe2x88x92j2xcfx80(fs)t]. According to this system, minimum value of a necessary sampling speed is 4. Therefore, the sampling speed in the system described in Japanese Patent Application Laid-Open No. 8-46658 is xc2xd of that disclosed in Japanese Patent Application Laid-Open No. 6-141048. As a result, it is possible to realize low power consumption of the receiver.
FIG. 20 is a structure diagram of a demodulator including a timing regenerating device that is similar to the demodulator described in the Japanese Patent Application Laid-Open No. 8-46658.
This demodulator mainly consists of antenna 100, frequency converting unit 200, first A/D converter 300a, second A/D converter 300b, timing regenerating device 400, and data deciding unit 500.
The timing regenerating device 400 includes VCO 401, timing phase difference calculating unit 402, Ich correlation calculating unit 403, Qch correlation calculating unit 404, and vector combination selecting unit 405.
Detailed structure of the vector combination selecting unit 405 will be explained with reference to FIG. 21.
The vector combination selecting unit 405 mainly consists of first vector combining unit 406a, second vector combining unit 406b, third vector combining unit 406c, fourth vector combining unit 406d, maximum absolute value detecting unit 407, and selecting unit 408.
How this demodulator demodulates a received preamble signal will be explained now.
First, the antenna 100 receives the preamble symbol of RF band. The frequency converting unit 200 frequency converts this preamble symbol of the RF band into a preamble symbol of a base band.
FIG. 22 is a signal space diagram showing a preamble symbol of this base band (for example, a xe2x80x9c1001xe2x80x9d pattern in the QPSK conversion system). In FIG. 22, xcex8c denotes, in degrees, a carrier phase of a reception signal. The preamble symbol shifts between a Nyquist point xe2x80x9cAxe2x80x9d and a Nyquist point xe2x80x9cBxe2x80x9d alternately through the origin for each one symbol in the drawing.
The vector angle of the Nyquist point xe2x80x9cAxe2x80x9d is xcex8c, and the vector angle of the Nyquist point xe2x80x9cBxe2x80x9d is (xcex8c+180). Difference between the vector angles of the Nyquist point xe2x80x9cAxe2x80x9d and the Nyquist point xe2x80x9cBxe2x80x9d is 180 degree.
The first A/D converter 300a receives the preamble symbol of the base band, samples the in-phase component of the preamble symbol at time t=xcfx84+iT/2 (where i=1, 2, 3, . . . , and xcfx84 represents a timing error (xe2x88x92T/2xe2x89xa6xcfx84 less than T/2), and T represents a symbol frequency), and outputs a sampled preamble data string Ipi (i=1, 2, 3, . . . ).
Similarly, the second A/D converter 300b receives the preamble symbol of the base band, samples the orthogonal component of the preamble symbol at the time t=xcfx84+iT/2, and outputs a sampled preamble data string Qpi (i=1, 2, 3, . . . ). The first A/D converter 300a and the second A/D converter 300b sample the data based on a sampling clock output from the timing regenerating device 400.
The timing regenerating device 400 calculates a timing error xcfx84 by using the sampled preamble data strings Ipi and Qpi (i=1, 2, 3, . . . ), and carries out a phase control for canceling the timing error xcfx84 to a regeneration sample clock and a regeneration symbol clock. The regeneration symbol clock is a clock of a symbol period having the regeneration sample clock frequency-divided into two.
The data deciding unit 500 receives the significant random data strings Idi and Qdi (i=1, 2, 3, . . . ) that follow the preambles after the timing error xcfx84 has been cancelled by the timing regenerating device 400, and latches the data at the Nyquist points by the regeneration symbol clock. Then, the data deciding unit 500 decides the data using the latched Nyquist point data, and outputs the demodulated data.
Detail operation of the timing regenerating device 400 will be explained now. First, the Ich correlation calculating unit 403 obtains correlation between each of the in-phase component I (t) and the orthogonal component Q (t) of the preamble symbol shown in FIG. 22 and a frequency component exp[xe2x88x92jxcfx80(fs)t] that is xc2xd of the symbol frequency, respectively. Specifically, the Ich correlation calculating unit 403 performs the calculation shown in the equations (1a) and (1b) with respect to the over-sampled preamble data string Ipi (i=1, 2, 3, . . . ):
Ici=Ipixc3x97cos xcfx80i/2xe2x80x83xe2x80x83(1a)
Isi=Ipixc3x97sin xcfx80i/2xe2x80x83xe2x80x83(1b)
Then, the Ich correlation calculating unit 403 calculates an average of the obtained results (Ici, Isi), thereby to obtain correlation values (CI, SI). Further, the Qch correlation calculating unit 404 performs the calculation shown in the equations (2a) and (2b) with respect to the over-sampled preamble data string QPi (i=1, 2, 3, . . . ) in a similar manner:
Qci=Qpixc3x97cos xcfx80i/2xe2x80x83xe2x80x83(2a)
Qsi=Qpixc3x97sin xcfx80i/2xe2x80x83xe2x80x83(2b)
Then, the Qch correlation calculating unit 404 calculates an average of the obtained results (Ici, Isi), thereby to obtain correlation values (CQ, SQ).
In the equations (1a), (1b), (2a), and (2b), cos xcfx80i/2=1, 0, xe2x88x921, 0, . . . , and sin xcfx80i/2=0, 1, 0, xe2x88x921, . . . . Therefore, it is easy to obtain the correlation values (CI, SI) and (CQ, SQ). For example, when averaging with four symbols, the correlation values (CI, SI) can be obtained from the equations (3a) and (3b) as follows:
CI=(Ipixe2x88x92Ipi+2+Ipi+4xe2x88x92Ipi+6+Ipi+8xe2x88x92Ipi+10+Ipi+12xe2x88x92Ipi+14)/8xe2x80x83xe2x80x83(3a)
SI=(Ipi+1xe2x88x92Ipi+3+Ipi+5xe2x88x92Ipi+7+Ipi+9xe2x88x92Ipi+11+Ipi+13xe2x88x92Ipi+15)/8xe2x80x83xe2x80x83(3b)
Correlation values (CQ, SQ) can be obtained from the equations (4a) and (4b) as follows:
CQ=(Qpixe2x88x92Qpi+2+Qpi+4xe2x88x92Qpi+6+Qpi+8xe2x88x92Qpi+10+Qpi+12xe2x88x92Qpi+14)/8xe2x80x83xe2x80x83(4a)
SQ=(Qpi+1xe2x88x92Qpi+3+Qpi+5xe2x88x92Qpi+7+Qpi+9xe2x88x92Qpi+11+Qpi+13xe2x88x92Qpi+15)/8xe2x80x83xe2x80x83(4b)
The vector angle between the correlation values (CI, SI), and the vector angle between the correlation values (CQ, SQ) both indicate timing phase errors. However, depending on the carrier phase xcex8c, both the vectors may be pointed in the same direction, opposite directions, or one vector may have a value equal to zero.
For example, for the preamble symbols at A and B that satisfy the range of xcex8c as (90 less than xcex8c less than 180) or (270 less than xcex8c less than 360) as shown in FIG. 22, when the Ich correlation calculating unit 403 samples at the timings of vertical lines shown in FIG. 23(a) and also when the Qch correlation calculating unit 404 samples at the timings of vertical lines shown in FIG. 23(b), data strings {Ipi, Ipi+1, Ipi+2, Ipi+3, . . . } and data strings {Qpi, Qpi+1, Qpi+2, Qpi+3, . . . } are obtained respectively. In this case, the correlation values (CI, SI) and (CQ, SQ) as shown in FIG. 24 are obtained, and the correlation vectors are pointed in opposite directions.
On the other hand, for the preamble symbols that satisfy the range of xcex8c as (0 less than xcex8c less than 90) or (180 less than xcex8c less than 270) as shown in FIG. 25, when the Ich correlation calculating unit 403 samples at similar timings as those in FIG. 23, that is, at timings of vertical lines shown in FIG. 26(a) and also when the Qch correlation calculating unit 404 samples at the timings of vertical lines shown in FIG. 26(b), data strings {Ipi, Ipi+1, Ipi+2, Ipi+3, . . . } and data strings {Qpi, Qpi+1, Qpi+2, Qpi+3, . . . } are obtained respectively. In this case, two correlation values of the correlation values (CI, SI) and correlation values (CQ, SQ) as shown in FIG. 27 are obtained, and the correlation vectors point toward the same direction.
Further, it is also clear that each vector length changes depending on the carrier phase xcex8c. When xcex8c={0, 180}, the vector corresponding to the correlation values (CI, SI) has a value equal to zero, and when xcex8c={90, xe2x88x9290}, the vector corresponding to the correlation values (CQ, SQ) has a value equal to zero.
The vector combination selecting unit 405 receives the correlation values (CI, SI) and (CQ, SQ), and combines them in four statuses respectively in order to reduce the influence of the carrier phase xcex8c. Then, the vector combination selecting unit 405 selects a combined vector having the highest SN ratio. The timing phase difference calculating unit 402 receives this combined vector, and calculates a timing phase.
Next, detail operation of the vector combination selecting unit 405 will be explained with reference to FIG. 21. The maximum absolute value detecting unit 407 obtains four absolute values of CI, CQ, SI and SQ of the correlation values (CI, SI) and (CQ, SQ), and detects a maximum of these the four absolute values.
The first vector combining unit 406a outputs combined vectors (G1c, G1s) based on following equations (5a) and (5b):
G1c=CI+sign[CI]xc2x7|CQ|xe2x80x83xe2x80x83(5a)
G1s=SI+sign[CIxc2x7CQ]xc2x7|SQ|xe2x80x83xe2x80x83(5b)
The second vector combining unit 406b outputs combined vectors (G2c, G2s) based on following equations (6a) and (6b):
G2c=CQ+sign[CQ]xc2x7|CI|xe2x80x83xe2x80x83(6a)
G2s=SQ+sign[CIxc2x7CQ]xc2x7|SI|xe2x80x83xe2x80x83(6b)
The third vector combining unit 406c outputs combined vectors (G3c, G3s) based on following equations (7a) and (7b):
G3c=CI+sign[SIxc2x7SQ]xc2x7|CQ|xe2x80x83xe2x80x83(7a)
G3s=SI+sign[SI]xc2x7|SQ|xe2x80x83xe2x80x83(7b)
The fourth vector combining unit 406d outputs combined vectors (G4c, G4s) based on following equations (8a) and (8b):
G4c=CQ+sign[SIxc2x7SQ]xc2x7|CI|xe2x80x83xe2x80x83(8a)
G4s=SQ+sign[SQ]xc2x7|SI|xe2x80x83xe2x80x83(8b)
In the above equations, the sign [*] expresses a sign {xe2x88x921, +1} of a numerical value within the brackets.
The selecting unit 408 receives a detection signal of the maximum absolute value detecting unit 407, and sets combined correlation values (xcexa3C, xcexa3S) as shown in following equations (9a), (9b), (9c), and (9d) respectively according to the status of a maximum value of the absolute values:
(xcexa3C, xcexa3S)=(G1c, G1s) (when |CI| is maximum)xe2x80x83xe2x80x83(9a)
(xcexa3C, xcexa3S)=(G2c, G2s) (when |CQ| maximum)xe2x80x83xe2x80x83(9b)
(xcexa3C, xcexa3S)=(G3c, G3s) (when |SI| is maximum)xe2x80x83xe2x80x83(9c)
(xcexa3C, xcexa3S)=(G4c, G4s) (when |SQ| is maximum)xe2x80x83xe2x80x83(9d)
Based on the above processing, the influence of the carrier phase xcex8c is removed, and the combined vector having the vector represented by the correlation values (CI, CQ) and (SI, SQ) set to the same direction is selected as a vector most suitable for estimating a timing phase.
For example, in the case of FIG. 24, the correlation values (CQ, SQ) having a smaller vector length are inverted to set both vector directions to the same direction, and the inverted correlation values (CQ, SQ) are added to the correlation values (CI, SI). Then, this combined vector is selected. In this case, the combined correlation values (xcexa3C, xcexa3S) become as shown in FIG. 28. In the case of FIG. 27, the correlation values (CQ, SQ) having a smaller vector length are added directly to the correlation values (CI, SI). Then, this combinedvector is selected. In this case, the combined correlation values (xcexa3C, xcexa3S) become as shown in FIG. 29.
It is also possible to structure the vector combination selecting unit 405 as shown in FIG. 30. In the case of the vector combination selecting unit 405 shown in FIG. 30, the vector combination selecting unit shown in FIG. 21 does not select one vector from the four vectors generated in advance from CI, SI, CQ and SQ. In stead, the vector combination selecting unit 405 selectively adds a result of first selecting unit 406a, a result of second selecting unit 406b, a result of third selecting unit 406c, and a result of fourth selecting unit 406d, based on a detection result of the maximum absolute value detecting unit 407. In this structure, it is possible to reduce the circuit scale as compared with the structure of FIG. 21. In FIG. 30, 409a denotes first adder, and 409b denotes second adder.
Next, the operation of the vector combination selecting unit 405 shown in FIG. 30 will be explained. First, the respective selecting unit output values of SEL1, SEL2, SEL3, and SEL4, based on the detection result of the maximum absolute value detecting unit 407. The details are as follows.
SEL1 output by the first selecting unit 406a has a value as represented by the following equations (10a) and (10b):
SEL1=CI (when |CI| or |SI| is maximum)xe2x80x83xe2x80x83(10a)
SEL1=CQ (when |CQ| or |SQ| is maximum)xe2x80x83xe2x80x83(10b)
SEL2 output by the first selecting unit 406b has a value as represented by the following equations (11a), (11b), (11c), and (11d):
SEL2=sign[CI]xc2x7|CQ| (when |CI| is maximum)xe2x80x83xe2x80x83(11a)
SEL2=sign[CQ]xc2x7|CI| (when |CQ| is maximum)xe2x80x83xe2x80x83(11b)
SEL2=sign[SIxc2x7SQ]xc2x7|CQ| (when |SI| is maximum)xe2x80x83xe2x80x83(11c)
SEL2=sign[SIxc2x7SQ]xc2x7|CI| (when |SQ| is maximum)xe2x80x83xe2x80x83(11d)
SEL3 output by the third selecting unit 406c has a value as represented by the following equations (12a), (12b), (12c), and (12d):
xe2x80x83SEL3=sign[CIxc2x7CQ]xc2x7|SQ| (when |CI| is maximum)xe2x80x83xe2x80x83(12a)
SEL3=sign[CIxc2x7CQ]xc2x7|SI| (when |CQ| is maximum)xe2x80x83xe2x80x83(12b)
SEL3=sign[SI]xc2x7|SQ| (when |SI| is maximum)xe2x80x83xe2x80x83(12c)
SEL3=sign[SQ]xc2x7|SI| (when |SQ| is maximum)xe2x80x83xe2x80x83(12d)
SEL4 output by the fourth selecting unit 406d has a value as represented by the following equations (13a) and (13b):
SEL4=SI (when |CI| or |SI| is maximum)xe2x80x83xe2x80x83(13a)
SEL4=SQ (when |CQ| or |SQ| is maximum)xe2x80x83xe2x80x83(13b)
The outputs SEL1 and SEL2 of the selecting units 406a and 406b is input into the first adder 109a. The outputs SEL3 and SEL4 of the selecting units 406c and 406d is input into the second adder 109b. The first adder 409a adds the values of SEL1 and SEL2, and outputs a result of the addition as xcexa3C. The second adder 409b adds the values of SEL3 and SEL4, and outputs a result of the addition as xcexa3S.
Thus, the vector combination selecting unit 405 shown in FIG. 30 outputs values similar to those of the vector combination selecting unit 405 having the structure shown in FIG. 21.
The timing phase difference calculating unit 402 receives the combined correlation values (xcexa3C, xcexa3S) obtained by the vector combination selecting unit shown in FIG. 21 and FIG. 30, and obtains the vector angle shown by the correlation values (xcexa3C, xcexa3S) based on the following equation (14):
xcex82s=tanxe2x88x921(xcexa3S/xcexa3C)xe2x80x83xe2x80x83(14)
where xcex82s represents a timing phase difference when normalization is carried out in the two-symbol period (2T). Therefore, when normalization is carried out in the symbol period (T), the timingphase difference xcex8s [deg] is obtained from the equation (15):
xcex8s=2xcex82s mod 360xe2x80x83xe2x80x83(15)
There is a difference of 180 [deg] between xcex82s shown in FIG. 28 and xcex82s shown in FIG. 29. However, based on the processing of the equation (15), the xcex8s obtained from the xcex82s in FIG. 28 and the xcex8s obtained from the xcex82s in FIG. 29 coincide with each other.
The relationship between the timing phase difference xcex8s and the timing error xcfx84 is as shown in the equations (16a) and (16b). When xcex8s greater than 180 [deg],
xcfx84=(xcex8sxe2x88x92360)T/360xe2x80x83xe2x80x83(16a),
and when xcex8sxe2x89xa6180 [deg],
xcfx84=(xcex8s)T/360xe2x80x83xe2x80x83(16b)
The timing phase difference calculating unit 402 gives a phase control signal for canceling the timing error xcfx84 to the VCO 401 at the latter stage, based on the timing error xcfx84 obtained using the equations (16a) and (16b).
The VCO 401 receives the phase control signal from the timing phase difference calculating unit 402, controls phases of the regeneration sample clock and the regeneration symbol clock, and sets the timing error xcfx84 to xe2x80x9c0xe2x80x9d. The regeneration symbol clock is generated based on the frequency division into two of the regeneration sample clock that has been phase-controlled by the control signal, for example.
As explained above, the conventional timing regenerating device 400 using the preamble calculates correlation between the xc2xd symbol frequency component included in the preamble symbol and the xc2xd symbol frequency component exp[xe2x88x92jxcfx80(fs)t] output from the VCO 401, and then estimates a timing phase from the vector angle shown by the correlation values. Further, as the sampling speed is a low speed of 2 [sample/symbol], this is an effective method particularly for the broadband TDMA radio communication system.
Although the vector combination selecting unit 405 reduces the influence of the carrier phase xcex8c, this timing regenerating device has had a problem that the precision of the calculation in the timing error xcfx84 is controlled by the carrier phase xcex8c.
In other words, the magnitude of the combined correlation values (xcexa3C, xcexa3S) output from the vector combining unit 405 becomes largest when the carrier phase xcex8c is {45, 135, 225, 315} [deg], and becomes smallest when the carrier phase xcex8c is {0, 90, 180, 270} [deg]. The ratio of these magnitudes becomes 21/2:1. Therefore, there arises such a phenomenon that the precision in the calculation of the timing error xcfx84 becomes best when the carrier phase xcex8c is {45, 135, 225, 315} [deg], and becomes worst when the carrier phase xcex8c is {0, 90, 180, 270} [deg].
When the preamble symbol having the carrier phase xcex8c=45 [deg] as shown in FIG. 31 is received at the timings of the vertical lines shown in FIG. 32, for example, the amplitude of the I component and the amplitude of the Q component of the preamble symbol becomes the same value (1/(21/2) of an envelope level, where the envelope level is a radius of a circle of the signal space diagram shown in FIG. 32). Therefore, the correlation values (CI, SI) at the I component side and the correlation values (CQ, SQ) at the Q component side become the same magnitude. The combined correlation values (xcexa3C, xcexa3S) in this case become the values obtained by synthesizing the correlation values (CI, SI) at the I component side with the correlation values (CQ, SQ) at the Q component side, as shown in FIG. 33(a)
On the other hand, when the preamble symbol having the carrierphase xcex8c=90 [deg] as shownin FIG. 34 is received at the timings of the vertical lines shown in FIG. 35, for example, the amplitude of the I component of the preamble symbol becomes xe2x80x9c0xe2x80x9d, and the amplitude of the Q component of the preamble symbol becomes the envelope level. Therefore, the correlation values (CI, SI) at the I component side becomes xe2x80x9c0xe2x80x9d, and the correlation values (CQ, SQ) at the Q component side become 21/2 times the correlation values when xcex8c=45 [deg]. The combined correlation values (xcexa3C, xcexa3S) in this case become the correlation values (CQ, SQ) at the Q component side because the correlation values (CI, SI) at the I component side becomes xe2x80x9c0xe2x80x9d, as shown in FIG. 33(b).
As a result, the ratio of the magnitude of the combined correlation values (xcexa3C, xcexa3S) when xcex8c=45 [deg] to the magnitude of the combined correlation values (xcexa3C, xcexa3S) when xcex8c=90 [deg] becomes 21/2:1. Therefore, it is clear that the SN ratio of the combined correlation values (xcexa3C, xcexa3S) when xcex8c=45 (or 125, 225, 315) [deg] becomes higher than the SN ratio of the combined correlation values (xcexa3C, xcexa3S) when xcex8c=90 (or 0, 180, 270) [deg]. Accordingly, in the conventional system, the precision in the calculation of the timing error xcfx84 when xcex8c=45 (or 125, 225, 315) [deg] becomes higher than the precision in the calculation of the timing error xcfx84 when xcex8c=90 (or 0, 180, 270) [deg].
Further, according to the conventional timing regenerating device, when the preamble symbol has a xc2xd symbol frequency component like the preamble symbol that shifts by xc2x190 [deg] at every one symbol as shown in FIG. 36, in addition to the preamble symbol that shifts by xc2x1180 [deg] at every one symbol as shown in FIG. 22, for example, it is possible to estimate a timing phase from any signal. However, in this case, there has also been a problem that the precision in the calculation of the timing error xcfx84 is influenced by the carrier phase xcex8c.
Further, the conventional timing regenerating device is effective only when the reception timing of a timing phase is known. For example, when the reception timing of a burst signal at the time of turning on the power supply to the mobile terminal or at the line reconnection time after recovery from a shadowing is unknown, it is not possible to know the reception timing of a preamble symbol. Therefore, it has not been possible to apply the conventional timing regenerating device.
It is an object of the present invention to provide a demodulator capable of calculating a timing error at high precision without receiving an influence of a carrier phase xcex8c.
Further, it is another object of the present invention to provide a demodulator that becomes valid when the reception timing of a preamble is not known, by simultaneously realizing an estimation of a timing phase using a preamble and a detection of the preamble.
Further, it is still another object of the present invention to provide a demodulator that realizes a high-speed synchronization and a high-speed resynchronization in a short preamble without receiving an influence of a carrier phase, and realizes a satisfactory BER (bit-error ratio) characteristics in a significant data section that follows the preamble, even when the reception timing of a burst signal that occurs at the power supply start-up time or at the reconnection timing after a recovery from a shadowing is unknown.
The timing regenerating device according to one aspect of the present invention comprises an in-phase component square calculation unit that receives a base band signal having a preamble symbol, calculates square of an in-phase component of the base band signal and outputs the squared in-phase component; an in-phase multiplier that multiplies a sign bit (xc2x11) of the in-phase component of the base band signal to the squared in-phase component and outputs the result as signed squared in-phase component; an orthogonal component square calculation unit that receives the base band signal, calculates square of an orthogonal component of the base band signal and outputs the squared orthogonal component; an orthogonal multiplier that multiplies a sign bit (xc2x11) of the orthogonal component of the base band signal to the squared orthogonal component and outputs the result as a signed squared orthogonal component; a squared-preamble in-phase correlation calculating unit that calculates correlation value between the signed squared in-phase component and a xc2xd symbol frequency component, and outputs the correlation value as an in-phase correlation signal; a squared-preamble orthogonal correlation calculating unit that calculates correlation value between the signed squared orthogonal component and the xc2xd symbol frequency component, and outputs the correlation value as an orthogonal correlation signal; a vector combination selecting unit that compares the magnitude of the in-phase correlation signal with the magnitude of the orthogonal correlation signal, matches the direction of a vector shown by the in-phase correlation signal or the orthogonal correlation signal whichever is smaller to the direction of a vector shown by the in-phase correlation signal or the orthogonal correlation signal whichever is larger, combines these signals, and outputs a correlation signal after the combination as a combined correlation signal; and a timing phase difference calculating unit that outputs a phase control signal from a vector angle shown by the combined correlation signal.
The timing regenerating device according to one aspect of the present invention comprises an in-phase component square calculation unit that receives a base band signal having a preamble symbol, calculates square of an in-phase component of the base band signal and outputs the squared in-phase component; an in-phase multiplier that multiplies a sign bit (xc2x11) of the in-phase component of the base band signal to the squared in-phase component and outputs the result as signed squared in-phase component; an orthogonal component square calculation unit that receives the base band signal, calculates square of an orthogonal component of the base band signal and outputs the squared orthogonal component; an orthogonal multiplier that multiplies a sign bit (xc2x11) of the orthogonal component of the base band signal to the squared orthogonal component and outputs the result as a signed squared orthogonalcomponent; a squared-preamble in-phase correlation calculating unit that calculates correlation value between the signed squared in-phase component and a xc2xd symbol frequency component, and outputs the correlation value as an in-phase correlation signal; a squared-preamble orthogonal correlation calculating unit that calculates correlation value between the signed squared orthogonal component and the xc2xd symbol frequency component, and outputs the correlation value as an orthogonal correlation signal; a vector combination selecting unit that compares the magnitude of the in-phase correlation signal with the magnitude of the orthogonal correlation signal, matches the direction of a vector shown by the in-phase correlation signal or the orthogonal correlation signal whichever is smaller to the direction of a vector shown by the in-phase correlation signal or the orthogonal correlation signal whichever is larger, combines these signals, and outputs a correlation signal after the combination as a combined correlation signal; and a preamble detecting/timing phase difference calculating unit that calculates a vector angle and a vector length of the combined correlation signal, decides that the preamble symbol has been detected when the vector length is larger than a predetermined threshold value, calculates a timing phase difference using a vector angle shown by the combined correlation signal at that time, and outputs a phase control signal.
Further, according to still another aspect of the invention, in the timing regenerating device of the above aspect, the timing regenerating device comprises a VCO that outputs a regeneration symbol clock, a regeneration sample clock, and a xc2xd symbol frequency component, based on a phase control signal. The base band signal to be input into the in-phase component square calculation unit and the orthogonal component square calculation unit is a signal that has been sampled based on the regeneration sample clock. The squared-preamble in-phase correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the VCO, and the squared-preamble orthogonal correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the VCO.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises a phase detecting unit that detects advancement/delay of a timing phase using the base band signal sampled based on the regeneration sample clock, and outputs detected signals as phase detection signals; and a phase detection signal averaging unit that calculates an average of the phase detection signals, and outputs the average as a phase advance/delay signal. The VCO outputs a regeneration symbol clock, a regeneration sample clock, and a xc2xd symbol frequency component, based on the phase control signal and the phase advance/delay signal.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises an oscillator that outputs an asynchronous sample clock and a xc2xd symbol frequency component. The base band signal to be input into the in-phase component square calculation unit and the orthogonal component square calculation unit is a signal that has been sampled by the asynchronous sample clock. The squared-preamble in-phase correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the oscillator, and the squared-preamble orthogonal correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the oscillator.
Also, the timing phase difference calculating unit calculates a timing phase difference from a squared root of the in-phase component of a combined correlation signal and a vector angle shown by a squared root of an orthogonal component of the combined correlation signal.
Further, according to still another aspect of the invention, in the timing regenerating device of the above aspect, the preamble detecting/timing phase difference calculating unit calculates a timing phase difference from a vector angle shown by a value obtained by multiplying a sign {xc2x11} of the in-phase component to a square root of an absolute value of an in-phase component of a combined correlation signal and a value obtained by multiplying a sign {xc2x11} of the orthogonal component to a square root of an absolute value of an orthogonal component of the combined correlation signal.
Further, the timing regenerating device according to still another aspect of the invention comprises an in-phase component square calculation unit that receives a base band signal having a preamble symbol, calculates square of an in-phase component of the base band signal and outputs the squared in-phase component; an in-phase multiplier that multiplies a sign bit (xc2x11) of the in-phase component of the base band signal to the squared in-phase component and outputs the result as signed squared in-phase component; an orthogonal component square calculation unit that receives the base band signal, calculates square of an orthogonal component of the base band signal and outputs the squared orthogonal component; an orthogonal multiplier that multiplies a sign bit (xc2x11) of the orthogonal component of the base band signal to the squared orthogonal component and outputs the result as a signed squared orthogonal component; an adder that adds the signed squared in-phase and orthogonal components, generates a squared addition signal using a result of this addition, and outputs this signal; a subtracter that subtracts the signed squared in-phase component from the signed squared orthogonal component or vice versa, and generates and outputs a squared subtraction signal using a result of this subtraction; a squared-addition signal component correlation calculating unit that calculates correlation value between the squared addition signal and a xc2xd symbol frequency component, and outputs this correlation value as an addition correlation signal; a squared-subtraction signal component correlation calculating unit that calculates correlation value between the squared subtraction signal and the xc2xd symbol frequency component, and outputs this correlation value as a subtraction correlation signal; a vector selecting unit that compares the magnitude of the addition correlation signal with the magnitude of the subtraction correlation signal, selects the addition correlation signal or the subtraction correlation signal whichever is larger, and outputs this signal as a selected correlation signal; and a timing phase difference calculating unit that outputs a phase control signal from a vector angle shown by the selected correlation signal.
Further, the timing regenerating device according to still another aspect of the invention comprises an in-phase component square calculation unit that receives a base band signal having a preamble symbol, calculates square of an in-phase component of the base band signal and outputs the squared in-phase component; an in-phase multiplier that multiplies a sign bit (xc2x11) of the in-phase component of the base band signal to the squared in-phase component and outputs the result as signed squared in-phase component; an orthogonal component square calculation unit that receives the base band signal, calculates square of an orthogonal component of the base band signal and outputs the squared orthogonal component; an orthogonal multiplier that multiplies a sign bit (xc2x11) of the orthogonal component of the base band signal to the squared orthogonal component and outputs the result as a signed squared orthogonal component; an adder that adds the signed squared in-phase and orthogonal components, generates a squared addition signal using a result of this addition, and outputs this signal; a subtracter that subtracts the signed squared in-phase component from the signed squared orthogonal component or vice versa, and generates and outputs a squared subtraction signal using a result of this subtraction; a squared-addition signal component correlation calculating unit that calculates correlation value between the squared addition signal and a xc2xd symbol frequency component, and outputs this correlation value as an addition correlation signal; a squared-subtraction signal component correlation calculating unit that calculates correlation value between the squared subtraction signal and the xc2xd symbol frequency component, and outputs this correlation value as a subtraction correlation signal; a vector selecting unit that compares the magnitude of the addition correlation signal with the magnitude of the subtraction correlation signal, selects the addition correlation signal or the subtraction correlation signal whichever is larger, and outputs this signal as a selected correlation signal; and a preamble detecting/timing phase difference calculating unit that calculates a vector angle and a vector length of the selected correlation signal, decides that the preamble symbol has been detected when the vector length is larger than a predetermined threshold value, calculates a timing phase difference using a vector angle shown by the selected correlation signal at that time, and outputs a phase control signal.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises a VCO that outputs a regeneration symbol clock, a regeneration sample clock, and a xc2xd symbol frequency component, based on a phase control signal. The base band signal to be input into the in-phase component square calculation unit and the orthogonal component square calculation unit is a signal that has been sampled based on the regeneration sample clock. The squared-addition signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the VCO, and the squared-subtraction signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the VCO.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises a phase detecting unit that detects advancement/delay of a timing phase using the base band signal sampled based on the regeneration sample clock, and outputs detected signals as phase detection signals; and a phase detection signal averaging unit that calculates an average of the phase detection signals, and outputs the average as a phase advance/delay signal, wherein the VCO outputs a regeneration symbol clock, a regeneration sample clock, and a xc2xd symbol frequency component, based on both the phase control signal and the phase advance/delay signal.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises an oscillator that outputs an asynchronous sample clock and a xc2xd symbol frequency component. The base band signal to be input into the in-phase component square calculation unit and the orthogonal component square calculation unit is a signal that has been sampled by the asynchronous sample clock. The squared-addition signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the oscillator. The squared-subtraction signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the oscillator.
Further, the timing regenerating device according to still another aspect of the invention comprises an in-phase component square calculation unit that receives a base band signal having a preamble symbol, calculates square of an in-phase component of the base band signal and outputs the squared in-phase component; an in-phase multiplier that multiplies a sign bit (xc2x11) of the in-phase component of the base band signal to the squared in-phase component and outputs the result as signed squared in-phase component; an orthogonal component square calculation unit that receives the base band signal, calculates square of an orthogonal component of the base band signal and outputs the squared orthogonal component; orthogonal multiplier that multiplies a sign bit (xc2x11) of the orthogonal component of the base band signal to the squared orthogonal component and outputs the result as a signed squared orthogonal component; an adder that adds the signed squared in-phase and orthogonal components, generates a squared addition signal using a result of this addition, and outputs this signal; a subtracter that subtracts the signed squared in-phase component from the signed squared orthogonal component or vice versa, and generates and outputs a squared subtraction signal using a result of this subtraction; a squared-addition signal component correlation calculating unit that calculates correlation value between the squared addition signal and a xc2xd symbol frequency component, and outputs this correlation value as an addition correlation signal; a squared-subtraction signal component correlation calculating unit that calculates correlation value between the squared subtraction signal and the xc2xd symbol frequency component, and outputs this correlation value as a subtraction correlation signal; a vector selecting unit that compares the magnitude of the addition correlation signal with the magnitude of the subtraction correlation signal, selects the addition correlation signal or the subtraction correlation signal whichever is larger, and outputs this signal as a selected correlation signal; a weighting unit that gives a weight corresponding to a magnitude of a vector length shown by the selected correlation signal to the selected correlation signal, and outputs the weighted selected correlation signal as a weighted correlation signal; an averaging unit that multiplies the weighted correlation signal by two, calculates an average of the signal, and outputs this average as a weighted average correlation signal; and a timing phase difference calculating unit that outputs a phase control signal from a vector angle shown by the weighted average correlation signal.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises a VCO that outputs a regeneration symbol clock, a regeneration sample clock, and a xc2xd symbol frequency component, based on a phase control signal. The base band signal to be input into the in-phase component square calculation unit and the orthogonal component square calculation unit is a signal that has been sampled based on the regeneration sample clock. The squared-addition signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the VCO, and the squared-subtraction signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the VCO.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises an oscillator that outputs an asynchronous sample clock and a xc2xd symbol frequency component. The base band signal to be input into the in-phase component square calculation unit and the orthogonal component square calculation unit is a signal that has been sampled by the asynchronous sample clock. The squared-addition signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the oscillator, and the squared-subtraction signal component correlation calculating unit calculates correlation value using the xc2xd symbol frequency component output from the oscillator.
Further, according to still another aspect of the invention, in the timing regenerating device of the above aspect, the adder adds a signed squared in-phase and orthogonal components to obtain a result as a squared addition signal, and the subtracter subtracts the signed squared in-phase component from the signed squared orthogonal component or vice versa, and obtains a result as a squared subtraction signal.
Further, according to still another aspect of the invention, in the timing regenerating device of the above aspect, the adder adds a signed squared in-phase and orthogonal components, and obtains a square root of this sum as a squared addition signal, and the subtracter subtracts the signed squared in-phase component from the signed squared orthogonal component or vice versa, and obtains a square root of this difference as a squared subtraction signal.
Further, according to still another aspect of the invention, in the timing regenerating device of the above aspect, when the in-phase component of a weighted correlation signal is negative, the averaging unit inverts the signs of the in-phase and orthogonal components of the weighted correlation signal respectively, and generates a correlation signal with the inverted signs as a first correlation signal. On the other hand, when the in-phase component of the weighted correlation signal is positive, the averaging unit generates this weighted correlation signal as a first correlation signal. Furthermore, when the orthogonal component of the weighted correlation signal is negative, the averaging unit inverts the signs of the in-phase and orthogonal components of the weighted correlation signal respectively, and generates a correlation signal with the inverted signs as a second correlation signal. On the other hand, when the orthogonal component of the weighted correlation signal is positive, the averaging unit generates this weighted correlation signal as a second correlation signal, and the averaging unit calculates an average of the first and second correlation signals respectively. Furthermore, when the vector length of the averaged first correlation signal is larger than the vector length of the averaged second correlation signal, the averaging unit outputs the averaged first correlation signal as the weighted average correlation signal. On the other hand, when the vector length of the averaged second correlation signal is larger than the vector length of the averaged first correlation signal, the averaging unit outputs the averaged second correlation signal as the weighted average correlation signal.
Further, according to still another aspect of the invention, the timing regenerating device of the above aspect further comprises a clip detecting unit that receives a base band signal having a preamble symbol, converts both the in-phase and orthogonal components of the base band signal into xe2x80x9c0xe2x80x9d when at least one value of in-phase and orthogonal components of the base band signal is outside a predetermined range, and outputs the base band signal straight when at least one value of in-phase and orthogonal components of the base band signal is within the predetermined range. The base band signal input into the in-phase component square calculation unit and the orthogonal component square calculation unit is the base band signal output from the clip detecting unit.
Further, the demodulator according to still another aspect of the invention comprises an antenna that receives a radio signal; a frequency converting unit that converts the frequency of the received radio signal into the frequency of a base band signal; an A/D converting unit that converts the base band signal into a digital base band signal based on a sampling at two times a symbol rate using a regeneration sample clock; a timing regenerating device; and a data deciding unit that extracts Nyquist point data from the digital base band signal using the regeneration symbol clock, decides the extracted Nyquist point data, and outputs the data as demodulated data.
Further, the demodulator according to still another aspect of the invention comprises an antenna that receives a radio signal; a frequency converting unit that converts the frequency of the received radio signal into the frequency of a base band signal; an A/D converting unit that converts the base band signal into a digital base band signal based on a sampling at two times a symbol rate using the asynchronous sample clock; a timing regenerating device; a data interpolating unit that interpolates the digital base band signal that has been sampled by the asynchronous sample clock, and outputs the interpolated data as an interpolated base band signal; and a data deciding unit that extracts a Nyquist point of the interpolated base band signal based on a phase control signal, decides data at the extracted Nyquist point, and outputs the data as demodulated data.